FastAPI

Why fastAPI

• a free UI to test your rest api - interactive API documentation systems, OpenAPI (Swagger) and JSON Schema standards
• Supposedly security and authentication is integrated
• Supposedly fast
• Editor support, useful for code editor autocompletion

Technologies

• REST
  • how you form your API
  • Representational State Transfer
  • Has an HTTP verb, a URL which related to a bit of data, and a parameterization of that
• Async
  • How you deliver it
  • Co-operative multitasking
  • Puts the onus on you to decide when the rest of your computer should be able to do stuff
  • Easy to get wrong
  • Easy to write code that will block the whole web application rather than make just one request slow
  • Excels in that it's able to deal with thousands and thousands of network sockets
• Dependency Injection (DI)

URL mapping

app = FastAPI()

@app.get( "/" )
def root( ... ):
   return {"greeting": "Hello world"}

app.include_router( events.router, prefix="/events"...)

router = APIRouter()

@router.post( "/", ..., status=201)
def create_object( ... ):
   ...

Getting stuff from requests: Path variables

• given this info
  • GET /events/1234?detail=full
  • Authorization: Token ABCD1234
• implicit way

@router.get( "/event/{id}" )
def get_object( id: int ):
  ...

• more explicit way - make things be required

from fastapi import Path
from pydantic import Required

@router.get( "/event/{id}" )
def get_object( id: int = Path(Required) ):
  ...

Getting stuff from URL requests: Query parameters

• given this info
  • GET /search/?text=something
  • Authorization: Token ABCD1234
• implicit way

@router.get( "/search" )
def search( text: str = None, offset: int = 0, limit: int = 100 ):
  ...

• more explicit way - make things be required

from fastapi import Query

@router.get( "/search" )
def search(
  text: str = Query( default=None, max_length=20 ),
  offset: int = Query( 0 ),
  limit: int = Query( 100 )
):

Data Validation: Pydantic

• Is this valid data??
• Throws helpful error messages if the data isn't formatted correctly
• "This field is required, but you didn't specify it."

from datatime import date as DateType
from enum import Enum
from pydantic import BaseModel

class Types( Enum ):
  done = 'DONE'
  cancelled = 'CANCELLED'

class Event( BaseModel ):
  date: DateType
  type: Types
  text: str

Extract blob of JSON that came in from request

from pydantic import Required

@router.post( "/events/" )
def create_object( event: Event = Required ):
   ...

Creating responses

• If you need to retun something, just return simple Python objects. The framework renders them to JSON for you

@app.get( "/" )
def root( ... ):
  return {"greeting": "Hello World" }

@app.post( "/events/". response_model=Event, status_code=201 )
def create_object( event: Event = Required ):
  ...
  return {
    "date": "2019-06-02",
    "type": "DONE",
    "text": "some stuff got done"
  }

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